This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Objective: To investigate whether sex differences exist in gene expression of LHRH as well as other neuronal systems known to influence LHRH neuronal activity. Luteinizing-hormone releasing hormone (LHRH) is a key regulator of reproductive function. Adult rhesus monkey (macaca mulatta) LHRH gene expression in the hypothalamus is regulated by gonadal steroids, primarily estrogens in females and androgens in males. Despite this distinction, there is no report of how sex-specific signals regulate LHRH gene expression. RNA and DNA were collected from the medial basal hypothalamus (MBH) and preoptic area (POA) of gonadally intact adult male (n=5, 11.0[unreadable]1.7 years of age) and female (n=5, 11.2[unreadable]2.0 years of age) rhesus monkeys. The phases of ovulatory cycle in the female monkeys were unknown, as they were obtained from the tissue distribution program. Using quantitative PCR, we found that LHRH mRNA levels in the MBH are significantly lower in males compared to females (p0.05), but there was no difference in the POA. Moreover, we found that there were no sex differences in GAD65, GAD67, NPY, KiSS-1, and GPR54 mRNA in either area. Because there is no permanent sexual differentiation in the primate hypothalamic LHRH neurosecretory system, i.e., LH surges could be induced by ovarian transplantation in orchidectomized adult male monkeys (Norman and Spies Endocrinology 118:2608-2610, 1986), it is possible that an epigenetic mechanism regulates the sex difference in LHRH gene expression. In the second experiment we investigated if CpG methylation, a covalent modification of DNA that influences transcription factor binding and gene expression, was different between the sexes. Preliminary investigations revealed a trend (p0.1) with males exhibiting higher CpG methylation than females in the 5'flanking region of the LHRH gene. This methylation is in a CpG rich region -2100/-1700 relative to the transcription start site in the rhesus LHRH gene. Collectively, these results indicate that there is a significant sex difference in LHRH mRNA levels in rhesus monkeys and that this may be related to a difference in CpG methylation. It is concluded that epigenomic modifications are factors in the complex orchestration of LHRH gene expression in primates. This research used WNPRC Animal Services (Pathology Services).